#define _CRT_SECURE_NO_WARNINGS 1
#include <cmath>
#include <iostream>
#include <string>
#include <vector>
#include <algorithm>
#include<math.h>
#include<stdlib.h>
#include<stdio.h>
#include<unordered_map>
using namespace std;

class Solution {
public:
    int missingNumber(vector<int>& nums) {
        int n = 0;
        for (int i = 1; i <= nums.size(); i++)
        {
            n ^= i;
        }
        for (auto& ch : nums)
        {
            n ^= ch;
        }
        return n;
    }
};

int main() {
    return 0;
}